How To Waterproof Your Shed

Water leaks can wreak havoc if they get inside your garden shed. Waterproofing is the only guarantee to protect both the structure and its contents. Don’t wait until the rain arrives to act, and follow our guide to take action now!

1. Inspect the building

A large blue shed with a bench in a shady garden
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The first thing on your agenda is to inspect your outdoor shed thoroughly. Look for any obvious places where water might be collecting. Below is a handy checklist of places to search and what to look out for:

  • Roof: This is where water ingress happens the most and with the greatest effect. Also, do a full inspection of the gutters and drains for holes or a build-up of rubbish.
  • Walls, doors, and windows: Check for any signs of holes, cracks, or signs of rot. Also, check if the windows come away from their frames or if the framing has gaps or is broken.
  • Gutter: Do a full inspection of the gutters and drains for holes or a build-up of rubbish.
  • Where the shed meets the floor: There could be gaps between the wall and the floor or base. These are areas where water can easily seep in.

You should have a clear idea of the areas where your shed is lacking and what you’ll need to focus on to address them by now. Once you’ve identified what needs fixing, let’s move on to solve the issues, shall we?

2. Secure the base or foundation

A small shed in a sunny garden
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It’s always a good idea to work from the bottom up, which means starting with the foundation. There are two ways to waterproof this area: 1.) use a raised base to elevate your shed off the ground, or 2.) lay a waterproof membrane underneath. Both methods effectively stop moisture from permeating below.

To install a raised base:

  1. Clear the area around your shed and remove any debris or vegetation. If necessary, level the ground using a shovel or rake to make it flat and compacted.
  2. Lift the shed (if needed) to install the raised base beneath it. For safety, use appropriate lifting equipment or ask for assistance.
  3. Begin placing the first row of your base material around the shed’s perimeter. Use a spirit level to ensure the concrete blocks or lumber are level and aligned.
  4. Continue adding rows until you reach your desired height. Stagger the joints for stability, especially if using concrete blocks.
  5. If using lumber, fasten the pieces together with screws or nails. For concrete blocks, ensure they fit tightly together, but don’t use glue if you need to move them later.
  6. Check for any gaps between the shed and the raised base. Seal these gaps with caulk or weatherproofing material to prevent water infiltration.
  7. Once the raised base is installed, carefully lower the shed back into its original place. Ensure it aligns properly with the raised base and sits securely on top.

Installing a membrane

A waterproof membrane is fitted underneath the shed and the surface it sits upon. The membrane is breathable, meaning it won’t hold water and become soggy, but it won’t let water pass through either.

To install the membrane, you need only place it between the shed and its base. However, the structure will already need to be on a solid surface, such as concrete or a raised base. If you don’t have one of these in your garden, a raised base might be easier to use.

Both options are sensible and effective to waterproof your shed base. Select the option that best suits your needs and situation.

3. Walls, windows, and doors

Next, it’s time to seal up the shed’s walls and fittings. Wooden material shrinks over time, causing cracks and gaps to open up in the structure. If you saw any in your initial inspection, now is the time to come back and clean them up properly.

Seal from the inside first. Fill gaps in the wood with silicone caulk. Pay special attention to the edges where two walls meet, as small gaps often appear there. You should also caulk around the windows if there are gaps in the frame using this shed window sealant.

Find any parts of the shed outside where the wood is decaying or wasting away. With a screwdriver or tool, remove the rotten wood and fill the void with wood filler. After all the gaps are filled and caulked, apply a layer of wood preservative to the outside walls and doors. This will keep the wood in good condition for longer.

4. The roof

Rainwater dripping off a shed roof
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Water ingress occurs most often on the roof, as it is the most exposed to water. Shed roofing should always be covered by mineral felt. It’s a lightweight material fitted over the shed roof to protect it from rain and other elements.

Feel free to follow the brief instructions below:

  • If you already have felt on your shed roofing, remove it and remove any dirt that has built up on it. It is best to do this when it is dry outside.
  • Measure the dimensions of where your roofing felt will go. Consider any overhang that your shed has.
  • Cut the felt to size and lay it over the shed to check sizing. Make any adjustments, then cover the back of the felt with bitumen paste. Bitumen will stick the felt to the roof without using nails, which creates holes for water to seep in through.
  • Stick the felt to the roof and smooth it down as much as possible. Any gaps or creases will allow water to accumulate.

A well-fitted roof felt covering can protect your shed from water ingress for years. For a more in-depth guide, check out our ‘How to Felt a Shed Roof’ guide next.


Despite what it might seem, waterproofing your garden building isn’t complicated. Using our guide, you should now have a completely waterproof shed!

If you have any further questions, please don’t hesitate to contact us at 01909 768840. Up next on your reading list: How to Damp Proof and Insulate a Garden Shed (Mega-Guide)

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